Final answer:
Work is being done in the subjects of Work and Energy and Conservation of Momentum.
Step-by-step explanation:
Work is being done in the subject of Work and Energy and Conservation of Momentum.
In Work and Energy, work is done when an external force is exerted on a system causing a component of the force to be parallel to its displacement. This results in a transfer of energy to or from the system. In Conservation of Momentum, work is done when an external force acts on a two-object system in linear motion, causing a change in the kinetic energy of the center of mass of the system.